102 lines
3.0 KiB
C
102 lines
3.0 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#include <stdarg.h>
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#include "portability.h"
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/*
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* vasprintf() and asprintf() for platforms with a C99-compliant
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* snprintf() - so that, if you format into a 1-byte buffer, it
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* will return how many characters it would have produced had
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* it been given an infinite-sized buffer.
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*/
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int
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pcap_vasprintf(char **strp, const char *format, va_list args)
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{
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char buf;
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int len;
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size_t str_size;
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char *str;
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int ret;
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/*
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* XXX - the C99 standard says, in section 7.19.6.5 "Thes
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* nprintf function":
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*
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* The snprintf function is equivalent to fprintf, except that
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* the output is written into an array (specified by argument s)
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* rather than to a stream. If n is zero, nothing is written,
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* and s may be a null pointer. Otherwise, output characters
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* beyond the n-1st are discarded rather than being written
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* to the array, and a null character is written at the end
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* of the characters actually written into the array.
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*
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* ...
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*
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* The snprintf function returns the number of characters that
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* would have been written had n been sufficiently large, not
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* counting the terminating null character, or a negative value
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* if an encoding error occurred. Thus, the null-terminated
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* output has been completely written if and only if the returned
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* value is nonnegative and less than n.
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*
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* That doesn't make it entirely clear whether, if a null buffer
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* pointer and a zero count are passed, it will return the number
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* of characters that would have been written had a buffer been
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* passed.
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*
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* And, even if C99 *does*, in fact, say it has to work, it
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* doesn't work in Solaris 8, for example - it returns -1 for
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* NULL/0, but returns the correct character count for a 1-byte
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* buffer.
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*
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* So we pass a one-character pointer in order to find out how
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* many characters this format and those arguments will need
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* without actually generating any more of those characters
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* than we need.
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*
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* (The fact that it might happen to work with GNU libc or with
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* various BSD libcs is completely uninteresting, as those tend
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* to have asprintf() already and thus don't even *need* this
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* code; this is for use in those UN*Xes that *don't* have
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* asprintf().)
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*/
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len = vsnprintf(&buf, sizeof buf, format, args);
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if (len == -1) {
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*strp = NULL;
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return (-1);
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}
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str_size = len + 1;
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str = malloc(str_size);
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if (str == NULL) {
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*strp = NULL;
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return (-1);
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}
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ret = vsnprintf(str, str_size, format, args);
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if (ret == -1) {
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free(str);
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*strp = NULL;
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return (-1);
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}
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*strp = str;
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/*
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* vsnprintf() shouldn't truncate the string, as we have
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* allocated a buffer large enough to hold the string, so its
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* return value should be the number of characters written.
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*/
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return (ret);
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}
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int
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pcap_asprintf(char **strp, const char *format, ...)
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{
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va_list args;
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int ret;
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va_start(args, format);
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ret = pcap_vasprintf(strp, format, args);
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va_end(args);
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return (ret);
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}
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